Method of fabricating flexible joints

ABSTRACT

A method of fabricating flexible joints such as are used in automotive steering linkages or the like wherein each housing is provided with an integral internal spherical bearing surface formed during the forging and inner cavity machining operations, with such housings being characterized by precisely localized hardened annular zones at the spherical bearing surfaces.

REFERENCE TO CO-PENDING APPLICATION

This application is a continuation-in-part of my co-pending application Ser. No. 663,273 filed Mar. 3, 1976 now U.S. Pat. No. 4,064,007.

BACKGROUND OF THE INVENTION

This invention relates generally to flexible joints and more particularly to a new and improved method of fabricating housings for ball joints such as are used in automotive steering linkages or the like.

PROBLEMS IN THE ART

It is presently the practice in the art to fabricate ball joints from forged housings provided with separate internal spherical bearing inserts for supporting the male ball studs. In many instances the spherical bearing inserts have been formed of synthetic resinous materials but a problem has been present in that such plastic bearing materials have been lacking in longevity under high stress operating conditions, particularly when operated in high temperature environments. Operation of automotive pivot joints in hot environments has only recently been dictated by the required pollution control devices added within the hood shells of the engine compartments.

In an effort to offset the high temperature environment problems, pivot joints have recently been fabricated with spherical bearings formed of annular metal inserts which overcome the heat problem but which require highly accurate machining operations both with respect to the fabrication of the metal inserts and the required annular seat supporting surface which must be accurately located and formed in the housing.

SUMMARY OF THE INVENTION

In general, the present invention comprises a novel method of producing pivot joint housings at high rates of production with such pivot joint housings including integrally formed spherical bearing surfaces which bearing surfaces are located and shaped simultaneously with the forging and internal machining of the housings, and by the formation of a localized annular hardened zone at the spherical bearing surface.

The localized hardened bearing zones are formed by an induction heating step precisely performed on the housing after the above mentioned forging and machining steps, and by a subsequent quenching whereby cooling fluid is precisely applied to the housing so as to maintain localization of the induction heating to a predetermined annular zone at the bearing surface. As a result, the metal in the balance of the housing remains non-hardened, tough, and fatigue resistant so as to be metallurgically proper for the main housing material.

As another aspect of the present invention, the method comprises the additional step of forming lubrication grooves in the spherical bearing surface by a coining operation performed in between the above-mentioned forging and machining operations. This provides grease reservoir grooves in the bearing surface without the presence of aberrations in the finished bearing surface.

As still another aspect of the present invention the above mentioned lubrication grooves are asymmetrically located with respect to the spherical bearing surface to prevent machine tool chatter during the final machining of the surface.

As another object of the present invention the pivot joint in one of its embodiments includes a novel method of fabricating ball studs wherein the lubrication grooves are formed in the spherical bearing surface of the ball stud during the forging thereof.

As still another object of the present invention the novel method in one of its embodiments comprises a novel ball stud construction which includes a forged head portion that includes a refined spherical bearing surface devoid of surface film and decarbonization.

It is, therefore, an object of the present invention to provide an improved method of fabricating pivot joints which include a housing portion provided with an integral spherical bearing surface surrounded by a localized hardened zone of high wear resistance, with the metal of the remainder of the housing portion being unhardened and metallurgically proper for a high degree of strength and fatigue resistance.

It is another object of the present invention to provide a method of the type described which utilizes an inductor electrode and quenching apparatus which are repeatedly locatable with respect to precise portions of the housing workpieces whereby the method is adaptable to high rates of industrial production and resulting low cost per unit.

It is still another object of the present invention to provide a method of fabricating pivot joints that includes a housing portion provided with integral hardened spherical bearing surfaces that include lubrication grooves located in the bearing surfaces without the presence of spherical aberrations adjacent the grooves.

It is another object of the present invention to provide a novel method of fabricating pivot joints of the type described that comprises a novel ball stud that includes lubrication grooves in the spherical bearing surface thereof, said grooves being integrally formed in the bearing surface during the forging thereof.

It is still another object of the present invention to provide a novel pivot joint construction of the type described that comprises a ball stud that includes a refined spherical bearing surface that is devoid of surface decarbonization and surface film normally resulting from the heat treating operation.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG 1 is a side sectional view of a ball joint including a housing constructed in accordance with the present invention;

FIG. 2 is a partial side elevational view of a workpiece used in forming the housing of FIG. 1;

FIGS. 3 through 5 are side elevational views, partially in section, of the workpiece of FIG. 2 in various steps of formation;

FIG. 6 is a bottom elevational view of the workpiece corresponding to FIG. 5;

FIG. 7 is an end sectional view of the workpiece of the preceding figures;

FIG. 8 is a side elevational view showing an induction heating electrode and an associated fixture for locating the workpiece of the preceding figures;

FIGS. 9 and 10 are side and end elevational views of a ball stud constructed in accordance with the present invention; and

FIGS. 11 and 12 are side and end elevational views of a second ball stud constructed in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring in detail to the drawings, FIG. 1 illustrates a typical pivot joint including a housing constructed in accordance with the present invention, with such housing being indicated generally at 10. The housing includes a cavity 12 that includes an inner wall surface 14 and a spherical bearing surface 16.

With continued reference to FIG. 1, a ball stud is indicated generally at 10. The housing includes a cavity 12 that includes an inner wall surface 14 and a spherical bearing surface 16.

With continued reference to FIG. 1, a ball stud indicated generally at 18 includes a ball shaped end 20 which is pivotally supported by bearing surface 16 as well as by a bearing surface 22 formed on a removable bearing insert 24.

Bearing insert 24 is urged inwardly by a compression spring 26 which is interposed between an end closure 28 and the bearing insert. The housing further includes a shank portion 30 as well as a top opening 32 which includes a tapered wall 34 the latter permitting angular movement of the shank 36 upon poviting thereof.

The assembly of FIG. 1 also includes a dust cover 38, sleeve 40, and nut 42.

Referring next to FIG. 2, the above mentioned housing 10 is formed from a workpiece W which consists of a rod of carbon steel with sufficient carbon content to permit subsequent induction hardening. A suitable steel material is referred to as the middle carbon type, such as SAE 1040.

After the workpiece W has been sheared to length from bar stock, it is heated and forged to the shape shown in FIG. 3 wherein the housing 10, with the cavity 12, have been forged to the shape illustrated.

The workpiece is next subjected to a coining operation to form the grease grooves 46 with such grooves being eccentrically located so as not to be directly opposite each other as seen in FIG. 6.

It is important to mention that during the forging operation, or when forging and coining operations are performed to include the grease grooves, then the surface carbon is removed as a result of the working of the metal during the forging or forging and coining steps.

It should further be pointed out that such surface decarbonization normally would inherently preclude the subsequent induction hardening of the wall portion of the housing where the spherical bearing is to be formed.

In accordance with the present invention the workpiece W is subjected to an internal machining operation using a circular milling cutter so as to machine away the surface decarbonization and accurately locate and finally shape and finish the previously mentioned spherical bearing surface 16. Inner wall portion 14 is also machined at the same time to remove the taper left by the forging die.

A bottom hole 32 is also formed in the housing as well as a groove 52 for receiving the end closure 28. Such bottom hole 32 and groove 52 can be cut at the same time the wall surface 14 and bearing surface 16 are machined.

It should further be mentioned that during the internal machining the grease grooves 46 are cut down in length and any surface aberrations present in FIG. 3 are machined away such that the bearing curvature will be accurately produced. As still another operation, a radial hole 54 is formed through the wall of the housing for the subsequent mounting of a grease fitting.

Reference is next made to FIG. 5 which illustrates the machining of the outwardly tapered surface 34 at the opening 32. The workpiece of FIGS. 5 through 7 is next positioned over an inductor electrode assembly indicated generally at 60 which includes an induction coil 62 and induction connector 64 mounted on a suitable supporting body 66.

The assembly of FIG. 8 further includes a lower positioning fixture 68 for receiving and positioning the bottom of housing 10 and an upper positioning fixture 70 for engaging and positioning the top of housing 10. The upper positioning fixture 70 is provided with extending and retracting mechanism as well as a spring loaded arrangement, not illustrated.

With continued reference to FIG. 8, the lower fixture is provided with a quenching inlet conduit 72 having radially extending outlet orifices indicated by dotted delineation at 74. When a coolant fluid is admitted under pressure into quench conduit 72, it is directed outwardly through the radial orifices 74 and impinges on the bearing surface 16. An alternate way of quenching can be effected by introducing the coolant through passage 71 in upper positioning fixture 70.

In operation, having been forged and finished to the configuration of FIG. 6, housing 10 is placed in the induction heating apparatus with the top of the supporting body 66 inserted into the cavity 12 of housing 10 such that the induction coil 62 is precisely positioned in close proximity to spherical bearing surface 16. The induction coil 62 is next energized with a predetermined appropriate amount of power to induction harden spherical bearing surface 16 and to also harden the underlying zone 80 to the predetermined depth.

It has been found that by using a SAE 1040 hot rolled steel with the forged area having a Brinell hardness of 143-229, then the depth of the hardened zone 80 should be formed with a zone depth of between 0.010 and 0.090 of an inch with the preferred range being between 0.020 and 0.080. This will produce a surface hardness of between 40 to 70 Rockwell C with the preferred range being between 50 and 60 Rockwell C. This depth of surface zone has been found to be ideal for both a wear resistant bearing surface and tough fatigue resistant housing.

Reference is next made to FIGS. 9 and 10 which illustrate a ball stud constructed in accordance with a modification of the present invention, with such stud being indicated generally at 118. In this embodiment the head portion 120 is provided with longitudinally extending lubrication grooves 124, instead of forming such lubrication grooves in the spherical bearing surface 16 of the housing portion as was the case with the previously described embodiment of FIGS. 1-6.

FIGS. 11 and 12 show a modified ball stud construction similar to the embodiment of FIGS. 9 and 10 except that the lubrication grooves 134 are of spirally extending configuration.

In both of the ball stud embodiments illustrated the spiral grooves are positioned so as not to be diametrically opposite one from another so as to eliminate vibratory machine chatter during a finish machining operation later to be described.

Reference is next made to FIGS. 9 and 10 which illustrate a ball stud constructed in accordance with a modification of the present invention and indicated generally at 118. In this embodiment the lubricating grooves 46 are eliminated from the housing seat 22 and instead are formed in the spherical outer surface of the ball stud.

Ball stud 118 is formed from a carbon steel blank which is cold headed to form an enlarged head portion on a shank portion 122 with the head portion including a spherical outer surface 120.

A plurality of spaced lubricating grooves 124 are formed in spherical outer surface 120 during the cold heading operation which forms the head portion on the ball stud. Such lubricating grooves 124 serve as cavities for retaining grease that maintains a film of lubricant at the confronting spherical bearing surfaces 120 on the stud and 22 on the housing.

It has been determined that in the production of certain designs of pivot joints, which include raised bottom shells, or webs, in the bottom of the housing forging, it is also possible to hot forge the flare or tapered wall 34 of the top opening 32 simultaneously with the hot forging of the housing portion 10. This eliminates the need for a separate machining operation to provide the flare 34 needed for angularity of stud movement. However, in such pivot joint designs where the flare 34 can be hot forged, it is not possible to also simultaneously forge the lubricating grooves 46. Hence, it becomes economically desirable to form the lubricating grooves 124 in the spherical outer surface 120 of the ball stud 118.

In accordance with the present invention, the ball stud 118 of FIGS. 9 and 10 can be economically and accurately produced by the following production steps:

1. A carbon steel blank is upset in a cold heading machine to form the shank portion 122 and enlarged head portion that includes the spherical outer surface 120, with the longitudinally extending lubricating grooves 124 being forged into surface 120 by a suitably shaped forging die.

2. The spherical outer surface 120 is next subjected to a machining operation, such as grinding, to accurately establish the spherical radius to specified tolerances for the particular job requirement. For example, with a one inch diameter ball a typical tolerance for automotive applications would be 0.5205-0.5165 spherical radius after grinding.

3. The workpiece is next heat treated to case harden the outer surface. A typical heat treatment would be to carbo-nitride in an atmospheric furnace with a temper at 400 degrees for one hour minimum at heat after quench. This will result in a case depth of 0.006-0.014 with the spherical surface file hard for the typical one inch diameter ball mentioned above.

4. The spherical outer surface 120 is next refined, preferably by a vibratory-slurry treatment wherein the heat treated workpieces are tumbled in a drum type container in the presence of a slurry of water and ceramic pellets. This polishing operation serves to refine the spherical surface by removing surface film which resulted from the above described heat treating operation.

After the finished ball studs 118 have been subjected to the above mentioned steps they are ready to be assembled into the pivot joint, as seen in FIG. 1, with the spherical outer surface 120 pivotally supported on the spherical bearing surface 22 of the housing portion 10.

FIGS. 11 and 12 illustrate a modified ball stud 128 which is identical to the previously described embodiment of FIGS. 9 and 10 except that the lubricating grooves 134 are of spiral configuration instead of straight as was the case with the prior embodiment.

It will be noted that in the case of both ball stud constructions the lubricating grooves are circumferentially spaced at 120 degrees so as to not be located diametrically opposite one another. It has been determined that this spacing arrangement eliminates the possiblity of vibratory chatter during the machining step.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred forms of embodiments of the invention are clearly shown. 

I claim:
 1. The method of making pivot joints comprising in combination, forging an electrically conductive workpiece of carbon steel to form a cup-shaped housing portion including a cavity provided with an inner wall having a bearing wall portion that includes a surface layer of decarbonized metal resulting from said forging machining said bearing wall portion to remove said layer of decarbonized metal and form a finished bearing surface having a carbon content compatible to induction hardening; mounting said workpiece in a locating fixture means including an inductor electrode disposed in said cavity in close proximity to said bearing surface; energizing said electrode to heat in a controlled manner to concentrate the heating effect of said electrode on said bearing surface and thereby harden an annular zone at said bearing surface, the metal in the balance of the housing surrounding said zone remaining non-hardened, tough and fatigue resistant; heading a carbon steel blank to form a ball stud comprising a spherical outer surface including lubricating grooves integrally formed during the heading operation; machining said spherical surface; heat treating said ball stud to case harden said spherical outer surface; surface finishing said ball stud to remove surface film from said spherical outer surface; and mounting said spherical outer surface of said ball stud on said bearing surface of said housing.
 2. The method of making pivot joints comprising, in combination, forging an electrically conductive workpiece of carbon steel to form a cup-shaped housing portion including a cavity provided with an inner wall having a bearing wall portion that includes a surface layer of decarbonized metal resulting from said forging machining said bearing wall portion to remove said layer of decarbonized metal and form a finished bearing surface having a carbon content compatible to induction hardening; mounting said workpiece in a locating fixture means including an inductor electrode disposed in said cavity in close proximity to said bearing surface; and energizing said electrode to heat in a controlled manner to concentrate the heating effect to said electrode on said bearing surface and thereby harden an annular zone at said bearing surface; applying a cooling fluid to said housing portion to limit the heating effect of said electrode to said annular zone, the metal in the balance of the housing surrounding said zone remaining non-hardened, tough and fatigue resisistant; heading a carbon steel blank to form a ball stud comprising a spherical outer surface including lubricating grooves integrally formed during the heading operation; machining said spherical surface; heat treating said ball stud to case harden said spherical outer surface; surface finishing said ball stud to remove surface film from said spherical outer surface of said ball stud on said bearing surface of said housing.
 3. The method defined in claim 1 that includes the step of coining lubrication grooves in said inner wall at the location of said finished bearing surface prior to the machining of said surface.
 4. The method defined in claim 1 wherein the predetermined thickness of said hardened annular zone is between 10 and 90 thousandths of an inch.
 5. The method defined in claim 1 wherein said annular zone is hardened to between 40 and 70 Rockwell C.
 6. The method defined in claim 2 that includes the step of coining lubrication grooves in said inner wall at the location of said bearing surface prior to the machining of said surface.
 7. The method defined in claim 2 wherein the predetermined thickness of said hardened annular zone is between 10 and 90 thousandths of an inch.
 8. The method defined in claim 2 wherein said annular zone is hardened to between 40 and 70 rockwell C. 